FIG. 1 is an exploded view of a prior art absolute microelectromechanical system (MEMS) pressure sensor 100. The absolute MEMS pressure sensor 100 comprises a plastic housing 102 having a port 104 that conducts pressurized fluid, typically a liquid, to an absolute MEMS pressure sensing element 106 located inside a pocket (or cavity) 108. The pocket 108 is located inside the plastic housing 102.
The pocket 108 holds the absolute MEMS pressure sensing element 106 and an application specific-integrated circuit (ASIC) 112. The absolute MEMS pressure sensing element 106 and the ASIC 112 are connected by thin bond wires 118. Different bond wires 116 connect the ASIC 112 to conductive lead frames 114. Chip capacitors 120 located outside the pocket 108 are connected across lead frames 114 and suppress electromagnetic interference. Electrical signals are provided to and received from the ASIC 112 through the metal “lead frames” 114, which extend through the plastic housing 102 up to the pocket 108.
Both the absolute MEMS pressure sensing element 106 and the ASIC 112 are encapsulated by a layer of viscous gel 110 inside the pocket 108. The gel 110 also protects the small-diameter bond wires 118 that conduct signals between components.
FIG. 2 is a cross-sectional view of the prior art absolute MEMS pressure sensor 100 shown in FIG. 1. The absolute pressure sensor module 100 comprises the absolute MEMS pressure sensing element 106 on top of a substrate or pedestal 202, which is mounted on the top side 207 of a housing substrate 204 using a thin layer of a pliable adhesive 206, typically silicone.
The absolute MEMS pressure sensing element 106 comprises a vacuumed cavity 210 formed between a thin diaphragm 205 and the substrate 202, which supports the absolute MEMS pressure sensing element 106. As is known, the diaphragm 205 deflects when pressure is applied to the diaphragm 205 through the gel 110. As is known, the deflection creates (changes) stress on a resistive Wheatstone bridge circuit (not shown) formed in the diaphragm 205. When a voltage is input to the Wheatstone bridge circuit, its output voltage changes responsive to the diaphragm's deflection thus converting the diaphragm's deflection into a measurable voltage change.
Both the ASIC 112 and the absolute MEMS pressure sensing element 106 are mounted to the housing substrate 204 using a pliable adhesive 206. A chip capacitor 120 connected between the lead frame 114 and a reference potential such as a ground (not shown) shunts undesirable high frequency noise signals to the reference potential.
Viscous gel 110 inside the pocket protects the pressure sensing element 106, the ASIC 112 and the bond wires from media contamination. Unfortunately, the gels used to protect components of a MEMS pressure sensor are expensive. Reducing the amount of gel required to cover and protect fragile components would be an improvement over the prior art.